Add a benchmark for exemplars

Author: bobrik

Cargo.toml

@@ -48,6 +48,10 @@ prost-build = { version = "0.12.0", optional = true }
 name = "baseline"
 harness = false
 
+[[bench]]
+name = "exemplars"
+harness = false
+
 [[bench]]
 name = "family"
 harness = false

benches/exemplars.rs

@@ -0,0 +1,37 @@
+use criterion::{criterion_group, criterion_main, Criterion};
+use prometheus_client::metrics::exemplar::HistogramWithExemplars;
+use prometheus_client::metrics::histogram::Histogram;
+
+type Exemplar = Vec<(String, String)>;
+
+const BUCKETS: &[f64] = &[1.0, 2.0, 3.0];
+
+pub fn exemplars(c: &mut Criterion) {
+    c.bench_function("histogram without exemplars", |b| {
+        let histogram = Histogram::new(BUCKETS.into_iter().copied());
+
+        b.iter(|| {
+            histogram.observe(1.0);
+        });
+    });
+
+    c.bench_function("histogram with exemplars (no exemplar passed)", |b| {
+        let histogram = HistogramWithExemplars::<Exemplar>::new(BUCKETS.into_iter().copied());
+
+        b.iter(|| {
+            histogram.observe(1.0, None);
+        });
+    });
+
+    c.bench_function("histogram with exemplars (some exemplar passed)", |b| {
+        let histogram = HistogramWithExemplars::<Exemplar>::new(BUCKETS.into_iter().copied());
+        let exemplar = vec![("TraceID".to_owned(), "deadfeed".to_owned())];
+
+        b.iter(|| {
+            histogram.observe(1.0, Some(exemplar.clone()));
+        });
+    });
+}
+
+criterion_group!(benches, exemplars);
+criterion_main!(benches);